Feb 19 (Reuters) - Low-cost carrier Spirit Airlines said it lost a bid for slots at Reagan National Airport in Washington that are being given up by American Airlines Group .

American Airlines, formed when US Airways merged with AMR Corp in December, had agreed to divest takeoff and landing rights at key U.S. airports under a settlement with the U.S. Justice Department, which had challenged the combination.

“We put in a bid at a price that we thought we could keep our target margin returns in place and we did not win,” Spirit Chief Executive Ben Baldanza said on a conference call to discuss the company’s fourth-quarter results.

Baldanza did not say who had won the slots, but said there were no more slots available at the airport.

Miramar, Florida-based Spirit is also interested in acquiring gates in Chicago, Los Angeles and Boston that are also being divested by American Airlines, Baldanza said.

American Airlines, the world’s largest carrier, agreed to divest 52 pairs of takeoff and landing rights, or 104 slots, at Reagan National Airport.

The carrier also agreed to give up gates at airports in Boston, Chicago, Dallas Love Field, Los Angeles and Miami.

Southwest Airlines Co has got 54 slots from American Airlines, while JetBlue Airways Corp has got 24. JetBlue also now owns 16 other slots that were previously under lease from American Airlines.

Spirit Airlines’ shares were up 5.4 percent at $50.23 in late morning trading on Wednesday after the company reported a fourth-quarter profit that beat analysts’ average estimate as it flew fuller planes.

The company earned 56 cents per share, excluding items, in the quarter ended Dec. 31. Analysts on average expected earnings of 50 cents per share, according to Thomson Reuters I/B/E/S.

The carrier’s load factor, which measures an airline’s success in filling its seats, rose to 86.2 percent in the quarter from 85.2 percent a year earlier.